In classical physics, light is viewed as part of the electromagnetic spectrum, traveling in the form of transverse waves. Quantum physics proposes that light is composed of quanta called

• A. photons
• B. electrons
• C. protons
• D. neutrinos

Answer: (A)

Light shows particle-like behavior in quantum physics when we think of it as composed of discrete energy packets. The quantum of the electromagnetic field is the photon, a massless particle that carries energy proportional to its frequency (E = hf) and momentum (p = hf/c). This quantization explains phenomena like the photoelectric effect and blackbody radiation, where light delivers energy in indivisible units rather than a continuous wave. The other particles listed—electrons, protons, and neutrinos—are distinct matter particles with different properties and do not serve as the quanta of light. Photons are the quanta of light and the carriers of electromagnetic interactions.